There is an increasing interest in InP epilayers for microwave devices and InGaAsP epilayers for photoelectronic emitters and detectors. The polished surfaces of InP used as substrates on which these epitaxial layers are grown, deteriorate at typical growth temperatures.
The InP slowly dissociates when heated above 450.degree. C. with the phosphorus passing as vapor into the surrounding hydrogen. The remaining indium coalesces into droplets and forms etch pits, typically a few micrometers deep, on the InP surface. The surface of the InP is no longer smooth and flat, and an epilayer grown on this substrate will both conform to the surface roughness and contain crystallographic defects which propagate from the damaged substrate surface. Most electronic device applications require an epilayer that is planar, defect-free and uniformly thick with thickness dimensions of 0.2 to 5 .mu.m. This planar geometry allows electrical conducting and gating contacts to be applied to the semiconducting layer surface with the use of photolithographic techniques to define both discrete and integrated device configurations. However, the surface must be smooth and flat for this technology. Crystallographic defects and nonuniform layer thickness degrade the electrical transport properties of the semiconductor by increased scattering of the charge carriers and inhomogeneity of the electrical field distribution. Epilayers that are free of surface roughness and defects are necessary for device quality semiconductor material.